一、阅读
1.B The problem made by heavy backpacks
2.B (students) have to carry heavy backpacks (楼主打错字了吧)
3.C may feel their backpacks are lighter
二、交际用语
4.B Never mind.没关系.
三、词汇与结构
5.A did
固定句型“It's (high/about) + that从句”中,that从句必须使用虚拟语气,即从句使用一般过去时或谓语由“should + 动词原形”构成,而且should不能省略.
另:该题答案也可以是:should do.